3,004,049 United States Patent Office Patented Oct. 10, 1961 1 2 acid or a salt thereof, lower reaction temperatures may 3,004,049 be employed and/or higher yields may be obtained and/or PRODUCTION OF ESTER TYPE ANONIC a highly improved, colorless product is obtained. Ab SURFACE ACTIVE AGENTS sence of color is of course highly important and critical Leslie M. Schenck, Mountainside, N.J., assignor to Gene in certain uses and the production of colorless products eral Aniline & Film Corporation, New York, N.Y., a has hitherto required relatively costly purification pro corporation of Delaware cedures. Such procedures may be eliminated by use of No Drawing. Fied Dec. 1, 1959, Ser'. No. 856,366 the process of this invention. 16 Claims. (C. 260-400) This invention accordingly comprises a process heat This invention relates to improvements in the produc ing at least 1 mole of an acylating agent selected from tion of ester type anionic surface active agents, and more O the group consisting of free aliphatic and alicyclic mono particularly to an improved process for preparing car carboxylic acids of at least 8 carbon atoms with 1 mole of boxylic acid esters of 2-hydroxyalkane sulfonic acids. an isethionate of the formula HO-CHR-CHR-SOM The reaction of carboxylic acid chlorides with 2-hy wherein R is selected from the group conisting of H and droxyethane sulfonic acid (isethionic acid) to produce lower alkyl and M is a cation selected from the group the corresponding esters is well known and is described 5 consisting of alkali metals and alkaline earth metals, at for example in U.S. Patents 1,881,172, 2,821,535 and an acidic pH and a temperature of about 140 to .320 C. other patents. The preparation of the acid chloride em in the presence of a catalytic amount of a compound se ployed as a reactant is not only hazardous but time con lected from the group consisting of hypophosphorous suming and costly, since it employs phosphorus tri acid and its salts, while removing the water formed dur chloride and requires at least one additional step. In 20 ing the reaction. addition, a considerable quantity of salt is concurrently When an excess of carboxylic acid is employed in the produced which is highly undesirable in many uses par present process, the final product will inherently contain ticularly when the resulting isethionic acid ester is em some free carboxylic acid which may if desired be re ployed in detergent and built soap formulations. Further, moved by common extraction or Superheated steam dis the salt in such formulations imparts thereto an unduly tillation procedures. However, a further advantage of high hygroscopicity and its removal is expensive. Still this process, in common with the processes disclosed in further, the hydrogen chloride produced as a result of the U.S. Patent 2,880,219 and in the above mentioned Ander reaction presents additional problems of corrosion an son et al. application, resides in the fact that the excess removal. carboxylic acid may be neutralized in situ with an in The reaction of 2-hydroxyalkane sulfonic acids with 30 organic or organic base such as the alkali metals or free carboxylic acids would of course eliminate a number amines such as triethanolamine or the like, to produce of the above mentioned disadvantages, and processes the corresponding soap in situ. The resulting mixture of employing such a reaction have in fact been proposed. soap and isethionate ester may be employed either di Thus, in U.S. Patent 2,635,103, a process is disclosed for rectly or after addition of other ingredients in the pro reacting one mole of the 2-hydroxyethane sulfonic acid 35 duction of detergent compositions and other surface with from more than 0.6 mole to less than one mole of active compositions in liquid or solid form. The use of a fatty acid at a temperature of 200-300° C. and at Sub such compositions in the formation of solid detergent atmospheric pressures in an inert atmosphere. This compositions in particulate or bar form is exceedingly process of course involves special handling and equip advantageous. These compositions may also be employed ment and in addition produces a product containing excess 40 in the production of skin creams, lotions, salves, and in isethionate salt which must for most uses be subsequently food products as foaming agents in addition to other uses removed. in which the presence of a mineral acid salt of an alkali In U.S. Patent 2,857,370 and in the copending appli metal, alkaline earth metal, ammonium or amine is un cation of . Anderson et al., Serial No. 603,214, filed desirable. August 10, 1956, processes are disclosed for the reaction 45 The duration of the reaction is generally inversely of one mole of 2-hydroxyalkane sulfonic acid salt with at proportional to the temperature employed, the rate of re least one mole of the carboxylic acid, in the presence of, action increasing as the temperature increases. However, respectively, a boron-containing compound or of a phos at higher temperatures, there is a tendency toward the phorus-containing compound selected from among a formation of colored by-products and the like while at specified group of such compounds. Although these proc 50 unduly low temperatures the reaction is too slow for esses are highly advantageous in eliminating the prob practically purposes. The process of this invention, as lem of removal of excess salt or isethionate and for vari pointed out above, permits the reaction to proceed at ous other reasons, they are still somewhat plagued with lower temperatures than hitherto possible although of the problems of undue color degradation of the product 55 course the temperature employed in any particular in and/or yields not as high as desired and/or the necessity stance will be dependent upon the particular acid em of employing relatively high reaction temperatures at ployed, the degree of purity of product desired, the rate of which degradation and other undesirable side reactions reaction desired, and the like. tend to occur. In general, temperatures of about 140-320 C. define It is an object of this invention to provide a process the extreme practical limits of operation, a range of about for preparing a carboxylic acid ester of a 2-hydroxy 60 160-230. C. yielding excellent results in most instances. alkane sulfonic acid which will not be subject to the At temperatures within the aforementioned ranges, the above disadvantages. Another object of this invention is reaction is usually complete in about 10 hours although the provision of an improved process for producing such the duration required for completion of the reaction may esters at lower reaction temperatures and/or higher yields range in any particular instance from about 2 to 15 and/or with decreased formation of colored byproducts. 65 hours. Other objects and advantages will appear as the descrip It is another advantage of this invention that an inert at tion proceeds. mosphere such as nitrogen, carbon dioxide or vacuum The attainment of the above objects is made possible need not be employed, and the reaction may be carried by my discovery that when the reaction between the out in air or even at super-atmospheric pressures. How carboxylic acid and the isethionic acid salt is carried out 70 ever, it is usually preferred for optimum results to carry in the presence of a catalytic amount of hypophosphorous out the reaction in the presence of an inert atmosphere 3,004,049 3 4. which may be maintained, for example, by use of Sub-at ammonium, mono-, di-, and trimethylamine, -ethylamine, mospheric pressures or an inert gas or vapor such as nitro -propylamine, -ethanolamine, and -propanolamine, pyri gen, carbon dioxide, or saturated or Superheated steam, dinyl, and morpholinyl hypophosphites. When hypophos the gas or vapor being preferably passed in continuous phorous acid is employed, it is preferred to use a 10 to manner over the reaction mixture to assist in removal of 50% aqueous solution thereof. the water formed during the reaction. The reaction must be carried out at an acidic pH, a The use of at least one mole of the carboxylic acid range of about 2.5 to 3.5 being preferred to assure opti acylating agent per mole of isethionate Salt (1:1 mini mum acceleration of the desired esterification reaction. mum molar ratio) is essential for the attainment of the The afore-mentioned amount of hypophosphorous acid desired results. In general, proportions of about 1.2 to O may suffice to bring the reaction medium to within the 2.5 moles of the acid per mole of isethionate Salt have desired pH range, or a second acid may be employed in been found sufficient in most instances, although up to 6 conjunction with the hypophosphorous acid or salt there to 10 moles or more of the acid may be employed where of. Any suitable acid may be employed for this purpose, a product containing a higher free carboxylic acid con inorganic acids such as phosphoric acid, hypophosphoric tent is desired. However, any increase in the amount of 5 acid, phosphorus acid, boric acid, fluoroboric acid, hydro excess carboxylic acid employed in the reaction mixture, chloric acid, sulfuric acid and the like being preferred. while to some extent aiding in fluidizing and Stabilizing It will be understood that the reactants and hypophos the reaction, at the same time tends to increase the cost phorous acid compound essential to the present process of the product due to greater heat requirements and in may be admixed in any order, although it is preferred to creased carboxylic acid loSSes. first mix the hypophosphorous acid compound with the As carboxylic acid acylating agents of at least 8 carbon carboxylic acid acylating agent and then slowly add the atoms which may be employed in the instant invention, isethionate salt reactant thereto. those preferred are of the aliphatic or alicyclic type al The inhibition of color formation in the product by the though aromatic acids may be used. Particularly pre addition of hypophosphorous acid or its salts is entirely ferred are the higher fatty acids of at least 8 carbon unexpected and very surprising based on other experi atoms. As representative of higher aliphatic and alicyclic mental data. In heat stability tests, fatty acids with an carboxylic acids operative in the instant invention, there intial VCS (Varnish Color Scale, Gardner Scale, Stand may be mentioned caprylic acid, pelargonic acid, capric ards of 1933) of 1 were admixed with, respectively, 1% acid, lauric acid, myristic acid, palmitic acid, Stearic acid, of sodium hypophosphite and 1% of hypophosphorous cleic acid, ricinoleic acid, linoleic acid, undecylenic acid, acid and subjected to temperatures of 160° C. for 6 tall oil acid, acid mixtures from various natural plant and hours. The treated samples as well as untreated controls animal oils such as olive, tallow, castor, peanut, coconut, showed the same degree of color degradation, namely a soybean, cotton seed, ucahuba, linseed, cod, herring, men VCS of 9. Further, when, instead of hypophosphorous haden, neatsfoot, sperm, palm, corn, butter, babassu, acid or its salts, the present reaction was carried out with kapok, hempseed, mustard, rubberseed, rape, safflower, 35 additions of 1 to 1.5% by weight of the fatty acid of other sesame, acids from the oxidation fractions of petroleum strong reducing agents, including titanous chloride and from oxo-aldehydes, naphthenic acids, abietic, acids, (TiCl3), hydroxylamine, stannous chloride, cobaltous and the hydrogenated derivatives of such acids and acid chloride, Sodium sulfite, Sodium bisulfite, sodium meta mixtures. Other acids which may be employed include arsenite (NaAsO2), and zinc dust, no beneficial effects on alkyl benzoic acids such as dodecyl benzoic acid, nonyl 40 the color of the products were obtained even though the benzoic acid, octyl benzoic acid, alkyl naphthoic acids above described pH requirements were maintained by use such as nonyl naphthoic acid, and the like. of phosphoric acid. The 2-hydroxyalkane sulfonic acids (isethionates, in The products of this invention may be employed in a cluding or and/or 6 lower alkyl substituted derivatives) multitude of uses wherever an anionic surface active agent employed in the form of their salts in the present process is called for, including the uses referred to in U.S. 2,880,- have the formula given above. In this formula, R may 45 219, column 5, line 30 to column 6, line 45. represent hydrogen, methyl or ethyl, and M may represent The following examples are illustrative of the present an alkaline earth metal Such as calcium, magnesium, or invention and are not to be regarded as limitative. All barium or preferably an alkali metal such as sodium or parts and proportions referred to herein and in the ap potassium. As examples of isethionic acids useful in the 50 pended claims are by weight unless otherwise indicated. form of their salts in the present process, there may be Example I mentioned isethionic acid, 2-hydroxypropane sulfonic acid, 2-hydroxy-3-butane sulfonic acid, 2-hydroxy-1-butane sul (A) Into a 1 liter electrically heated fusion pot fitted fonic acid and the like. These salts are preferably em With an agitator, thermometer, dropping funnel, distilla ployed in the form of dry powders, but they may also be 55 tion condenser and inlet for inert gas is charged: 300 g, employed as aqueous Solutions since the water is removed coconut fatty acid (1.41 moles, M.W. 212) and 8 g. 50% from the reaction medium together with the water formed hypophosphorous acid (4 g. 100%=1.33% by weight of as a result of the reaction in accordance with this process. fatty acid charged). The reaction mixture is heated to An essential feature of this invention resides in the 200 C. under a slow stream of nitrogen to remove mois addition to the reaction medium of a small, effective or 60 ture, and there is added over five minutes with agitation catalytic amount of hypophosphorous acid or a salt there 103.5 g. sodium isethionate (0.7 mole, M.W. 148). The of. Generally about 0.1 to 10%, and preferably about reaction mixture is agitated two hours at 200° C. at the 0.3 to 1.5% of such acid or salt, based on the weight of end of which time the mixture by analysis contains 0.69 the carboxylic acid acylating agent, is sufficient to provide mole of the coconut fatty acid ester of sodium isethionate the desired improvements in lower reaction temperatures 65 (236.2g. 100% ester, M.W. 342). The product, obtained and/or prevention of color degradation of the product in over 99% of the theoretical yield, based on the sodium and/or increased yields and the like. Hypophosphorous isethionate, has a pH of 3.2 as a 10% slurry in 1:1 iso acid and its alkali metal salts, e.g. sodium and potassium propanol-water. The pH is adjusted to 7.0 by mechanical Salts are generally preferred although any metal (including admixture with sodium hydroxide, and a 2.5% solution alkali metal and alkaline earth metal), ammonium or 70 of the resultant free-flowing dry powder gives a APHA amine salt of the hypophosphorous acid may be em color of 3. ployed. These salts may be employed in their hydrated (B) As a control, Example 1A is repeated substituting or dehydrated form. As examples of such salts, there 6.2 g. 85% phosphoric acid for the 8 g. 50% hypophos may be mentioned aluminum, cadmium, sodium, potas phorous acid. After two hours heating at 200° C., there sium, lithium, calcium, strontium, barium, magnesium, 75 is obtained by analysis 0.603 mole of the sodium isethi 3,004,049 5 6 onate ester of coconut fatty acid (206 g. 100% ester, acid ester of sodium-6-methylisethionate is obtained. The M.W. 342). A 10% slurry of the product in 1:1 dis product, with a pH of 3.3, has an APHA color of 8 when tilled water-isopropanol has a pH of 3.15. Upon neu examined as a 2.5% solution. tralization to pH 7 with sodium hydroxide, the APHA (B) Operating as in 5A, with the exception that 1 g. color of a 2.5% solution is found to be 63. 85% phosphoric acid is substituted for the hypophos phorous acid, an APHA color of 53 on a 2.5% solution Example 2 of the product is observed, and less than 50% conversion Example 1A is repeated, with the exception that the of the sodium-6-methylisethionate to the desired stearic reaction mixture is agitated at 155 C. until by analysis acid ester is accomplished. 93.2% of the sodium isethionate charged is converted to O This invention has been disclosed with respect to certain the corresponding coconut fatty acid ester of sodium preferred embodiments, and there will become obvious to isethionate. The APHA color of a 2.5% solution is persons skilled in the art various modifications, equiv found to be 5. alents or variations thereof which are intended to be Example 3 included within the spirit and scope of this invention. 5 I claim: (A) An admixture of 285 g. tallow fatty acid (1 mole, 1. A process comprising heating at least 1 mole of an M.W. 285), 2.85 g. 50% hypophosphorous acid (0.5% acylating agent selected from the group consisting of by weight based on the fatty acid charged) and 97.6 g. free aliphatic and alicyclic monocarboxylic acids of from (0.66 mole) of sodium isethionate is agitated at 230 C. 8 to 22 carbon atoms with 1 mole of an isethionate of for one hour at 240 mm. pressure to assist in remov 20 the formula HO-CHR-CHR-SOM wherein R is ing the water formed during the esterification. There is Selected from the group consisting of H and lower alkyl obtained by analysis 265 g. (0.64 mole, M.W. 415) of and M is a cation selected from the group consisting of the tallow fatty acid ester of sodium isethionate, repre alkali metals and alkaline earth metals, at an acidic pH senting 97% of the theoretical yield. The product, with and a temperature of about 140 to 320° C. in the presence a pH of 2.7, has an APHA color of 7 as a 2.5% solution. of a catalytic amount of a compound selected from the (B) Operating as in 3A with the exception that the group consisting of hypophosphorous acid and its metal, 2.85 g. 50% hypophosphorous acid are eliminated from ammonium and amine salts, while removing the water the reaction mixture, there is obtained by analysis 138 g. formed during the reaction. (0.33 mole) of the tallow fatty acid ester of sodium 2. A process as defined in claim 1 wherein the acylating isethionate. This product, with a pH 5.5, has an APHA 30 agent is a fatty acid. color of over 100 as a 2.5% solution. 3. A process as defined in claim 1 wherein the isethi Example 4 onate is sodium isethionate. (A) An admixture of 345 g. coconut fatty acid (1.4 4. A process as defined in claim 1 wherein the isethi moles) 4 g. sodium hypophosphite and 103.5 g. sodium onate is sodium-3-methylisethionate. isethionate (0.7 mole) is agitated 10 hours at 160° C. 35 5. A process as defined in claim 1 wherein said com Upon analysis, the reaction mixture is found to contain pound is hypophosphorous acid. 50.4 g. (0.147 mole) of the sodium salt of the isethionic 6. A process as defined in claim 1 wherein said com acid ester of coconut fatty acid representing 21% of the pound is sodium hypophosphite. theoretical conversion. The mixture has a pH of 4.4, 40 7. A process as defined in claim 1 wherein the pH and the APHA color of a 2.5% solution is 4. ranges from about 2.5 to 3.5. (B) Operating in the identical manner in 4A, with 8. A process as defined in claim 1 wherein about 1.2 the exception that 8.5 g. phosphoric acid 85% are added to 2.5 moles of the acylating agent are heated with 1 mole to reduce the pH of the reaction mixture to 2.9, there is of the isethionate. obtained 234 g. (.685 mole) of the sodium salt of the 9. A process as defined in claim 1 wherein the tem isethionic acid ester of coconut fatty acid representing 45 perature is about 160 to 230° C. 98% of the theoretical conversion. The APHA color 10. A process comprising heating at least 1 mole of a of a 2.5% solution of the product is 5. fatty acid of from 8 to 22 carbon atoms with 1 mole of (C) Operating in the identical manner of 4A, with a sodium isethionate at a pH of about 2.5 to 3.5 in the the exception that the 4 g. sodium hypophosphite are 50 presence of a catalytic amount of a compound selected eliminated, there is obtained by analysis 53.7 g. (.157 from the group consisting of hypophosphorous acid and mole) of the sodium salt of the isethionic ester of coco its metal, ammonium and amine salts while removing nut fatty acid representing 22.1% of the theoretical the water formed during the reaction. conversion. The product has a pH of 4.8, and the APHA 11. A process as defined in claim 10 wherein said color of a 2.5% solution is 71. 55 compound is hypophosphorous acid. (D) Operating in an identical manner as in 4A, with 12. A process as defined in claim 10 wherein said the exception that the 4 g. sodium hypophosphite are re compound is sodium hypophosphite. placed with 8.5 g. 85% phosphoric acid, there is obtained 13. A process as defined in claim 10 wherein the 217 g. (.635 mole) of the coconut fatty acid ester of temperature is about 160 to 230 C, sodium isethionate, representing 90.6% of the theoretical 60 14. A process as defined in claim 10 wherein said yield. The product has a pH of 3.0 in 1:1 isopropanol compound is employed in an amount ranging from about Water, and the APHA color of a 2.5% solution is 48. 0.3 to 1.5% by weight of the fatty acid. 15. A process as defined in claim 1 wherein said Example 5 compound is an alkali metal salt of hypophosphorous acid. (A) Operating as in Example 1A, an admixture of 65 16. A process as defined in claim 10 wherein said 274 g. commercial stearic acid (1 mole), 1.6 g. 50% compound is an alkali metal salt of hypophosphorous hypophosphorous acid and 113.4 g (0.7 mole) sodium acid. g-methylisethionate is reacted at 210 C., and 97% of No references cited. the theoretical conversion of the isethionate to the stearic